Is the center of left and right between the US left and right or in general? Even without the overton window the US left is mostly dems who support corporations and occasionally throw social programs in as well, while the right is teetering on fascism. If you're looking at all of US history there are periods where social programs, workers rights, and higher taxes on the rich had more support, but again you'd have to balance that with the historic fascism.

If you're talking in general, do you look at the furthest left and right political philosophies to ever have been implemented? Because while you can get leftist policies beyond what the US does, you've still got the nazis to contend with. So I guess I'm still not really sure where a centrist of your stripe is looking when deciding what center line to walk.